2.3. Measurement of contents in medium
An aliquot of culture broth was withdrawn to check cell number and viability, and to measure the amount of nutrient remaining and amount of metabolites produced. Cell number and viability were measured by Cell Counter (Bio-Rad). Residual glucose and production of lactate, glutamine, glutamate, and ammonium salt in sampled broth were measured by multifunctional biosensor BF-7D (Oji Scientific Instruments, Japan). LDH activity was measured by LDH assay kit (Wako Chemical, Japan) according to the manufacturer’s instruction. Activity of human tissue plasminogen activator (tPA) was measured by colorimetric method using S-2288 (Diapharma, USA), as described previously (Feng, 1995).